Probing particle-particle interactions in flocculated oil-in-water emulsions using ultrasonic attenuation spectrometry

The flocculation of silicone oil-in-water emulsions (phi = 0.1) containing quasi-monodisperse droplets was studied by ultrasound. The ultrasonic atten uation spectra of emulsions with different particle sizes (200-1600 nm) wer e measured between 0.5 and 10 MHz using an interferometer. Flocculation was induced by adding excess sodium dodecyl sulphate micelles to the emulsions to increase the attractive forces between the droplets. Droplet flocculati on decreased the ultrasonic attenuation at low frequencies because of overl ap of the thermal waves caused by the close proximity of the droplets withi n the Aocs. A mean-field model which takes into account this effect was use d to determine the droplet volume fraction within the flocs and thus to est imate the distance between the droplets.